/?.> 


;  /  >   u 


lpril25, 1912. 


U.  S.  DEPARTMENT  OF  AGRICULTURE 

BUREAU  OF  ENTOMOLOGY     CIRCULAR  No.  150. 

L.  O.  HOWARD.  Entomologist  and  Chief  of  Burecu. 


THE  RED  SPIDER  ON  (X)TTON. 


bY 


E.  A.  MCGREGOR, 

Si  i<  rUifie  Assi 


32120       Clr.  150      L2 


WASHINGTON  :  GOVERNMENT  PRINTING  I 


BUREAU   OF  EXTOMOLOGY. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stand  product  insect  investigations. 

A.  D.  Hopkins,  //*  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  fgrag(   insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F,  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 

Mabel  Colcord,  in.  charge  of  library. 

Southern  Field  Crop  Insect  Investigations. 
W.  I).  Hunter,  in  charge. 

F.  C.  Bishopp,  A.  II.  Jennings,  H.  1".  Wood,  W.  V.  King,  engaged  in  tick  life- 
history  investigations. 

W.  D.  Pierce,  G.  D.  Smith,  J.  D.  Mitchell,  Harry  I'inkus.  R.  R.  Coad,  R.  W. 

Moreland,  engaged  in  cotton-boll  weevil  investigations. 
A.  C.  Morgan,  G.  A.  Runner,  S.  E.  Ckumb,  D.  C.  Parman,  engaged  in  tobacco 

insect  investigations. 
T.  E.  Holloway,  E.  R.  Barber,  engaged  in  sugar-cane  insect  investigations. 

E.  A.  McGregor,  W.  A.  Thomas,  engaged  in  red  spider  and  other  cotton  insect 
investigations. 

J.  L.  Webb,  engaged  in  rice  insect  investigations. 

R.  A.  Cooley,  D.  L.  Van  Dine,  A.  F.  Conbadi,  C.  C.  Krumbiiaar.  collaborators. 

n 


Circular  No.  150. 


I--u.  d  April '25,  1912 


United  States  Department  of  Agriculture, 

BUREAU   OF  ENTOMOLOGY, 
L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


THE  BED  SPIDER  ON  COTTON.1 

•  -anychua  bimaculatus  Harvej   | 

By    K.    A.    M<  i  rBl  GOB, 

Scientific  Assistant. 
IN  CRODl  I    rORY. 

The  minute,  reddish  spinning  mite  commonly  known  as  .the  red 
spider  is  rapidly  assuming  a  position  of  importance  among  cotton 
pests.  At  Batesburg,  S.  C,  in  L911,  it 
first  became  noticeable  on  cotton  about 
June  1.  causing  little  more  than  passing 
notice  at  that  time  among  the  farmers, 
hut  by  the  1st  of  .Inly  it  had  increased  so 
enormously  that  the  effect  upon  cotton 
in  certain  places  was  most  alarming. 
Season-  of  excessive  drought  greatly  fa 
vor  the  multiplication  of  the  mites  until 
the  resulting  injuries  are  often  so  severe 
as  to  cause  the  death  of  many  plants. 

Red-spider  infestation  is  frequently 
miscalled  "  rust  "  by  farmers,  since  in- 
fested Leaves  soon  turn  deep  red  on  their 
upper  surface  Such  leaves,  however,  if 
examined  underneath,  reveal  the  pres- 
ence of  the  red  spiders  and  the  incon- 
spicuous webs  behind  which  the}'  are 
feeding  and  laying  their  eggs. 


HISTORY    AND    IMS  lit  MUTTON. 


I'n:.    1.     'I'h.'    red    spider,     Tet- 
ranychus    bimaculatus:    Adult 
Female.        Greatly      enl 
i  Banks.) 


With  the  exception  of  an  outbreak  in 
Louisiana,  reported  by  Prof.  II.  A.  Mor- 
gan   in    IS!)!'),   severe    Occurrence    of    the    cotton    red    spider    had    not 

been  reported  until  L903,  at  which  time  complaints  of  damage  came 

1  This  circular  i-  based  primarily  upon  wort  done  at  Batesburg,  s.  c.  in  1911, 
under  the  direction  "f  Mr.  \v.  D.  Hunter,  but  also  Includes  the  results  of  observations 
bj    Messrs.  Q    a    Runner  mid  II.  l\  Wilson  during  the  two  preceding 


2  THE   RED    SPIDER    ON    COTTON. 

from  South  Carolina  and  Georgia.  In  1904  Mr.  E.  S.  G.  Titus,1 
then  of  this  bureau,  found  severe  infestation  in  fields  about  Bates- 
burg,  S.  C.j  and  the  following  year  he  reported  severe  injury  in 
North  Carolina,  South  Carolina,  Georgia,  and  Alabama.  Since 
then  the  additional  records  of  Dr.  F.  H.  Chittenden  2  and  Messrs. 
G.  P.  Weldon,  D.  T.  Fullaway,  and  others  establish  the  presence 
of  the  common  red  spider  in  Maine.  Massachusetts,  New  York.  New 
Jersey,  District  of  Columbia,  Virginia,  North  Carolina,  South  Caro- 
lina, Georgia,  Florida,  Alabama,  Mississippi.  Louisiana.  Texas.  Ohio, 
western  Colorado,  Wyoming,  Idaho,  "Washington,  California,  and 
the  Hawaiian  Islands. 

The  red  spider  was  described  by  Harvey3  in  1893  as  Tetranychus 
8-maculatus.  Harvey  considered  it  quite  distinct  from  the  European 
species  T.  telarius  L.  His  types  were  from  Orono,  Me.  In  1907  Prof. 
H.  A.  Morgan  published  observations  on  the  cotton  mite,  and  ap- 
parently accepted  the  determination  of  the  species  as  T.  telarius. 
In  1900  Mr.  Nathan  Banks  described  the  cotton  mite  under  a  dis- 
tinct name — Tetranychus  gloveri — but  from  the  study  of  additional 
specimens  has  now  concluded  that  the  name  is  synonymous  with 
Harvey's  T.  bimaculatus.  Specimens  of  red  spiders  on  cotton  from 
South  Carolina  have  upon  two  recent  occasions  been  determined  by 
Prof.  A.  Berlese  as  the  continental  species — Tetranychus  telarius. 
As  there  seems  to  be  considerable  doubt  on  this  point,  we  shall  follow 
Mr.  Banks  in  considering  the  form  with  which  we  are  dealing  as 
Tetranyc  Jinx  bimaculatus, 

DESCRIPTION. 

The  typical  female  (fig.  1)  is  0.46  mm.  long  by  0.24  mm.  wide, 
broad-oval,  widest  in  front,  and  the  legs  are  shorter  than  the  body. 
Its  color  is  usually  brick-red.  The  typical  male  is  0.27  mm.  long  by 
0.15  mm.  wide,  oval-wedge  shape,  narrowed  behind,  the  legs  about 
equaling  the  length  of  the  body,  and  its  color  is  usually  reddish 
amber.  Individuals  of  both  sexes  usually  possess  on  either  side  of 
the  body  a  dark  spot,  caused  by  the  food  contents.  This  spot  may 
vary  greatly  in  color,  size,  and  outline.  Similarly,  depending  upon 
the  host  plant  and  upon  locality,  the  general  color  of  the  red  spider 
is  subject  to  great  variation. 

The  eggs  are  very  minute,  but  in  proportion  to  the  mites  they  are 
large.  They  are  perfectly  round,  and  when  first  laid  are  as  clear  as 
water.  Each  female  lays  (in  the  months  of  June.  July,  and  August) 
about  50  to  60  eggs,  depositing  about  6  per  day  for  a  period  of  about 
nine  days.    Less  than  3  eggs  or  more  than  9  are  rarely  deposited  each 

'  Cir.  65,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  1905. 

-Cir.  104,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  1905. 

a  Ann.  Kept.  Maine  Agr.  Exp.  Sta.  for  1892,  Pt.  IV,  pp.  i::.i-14G. 


THE    RED   SPIDER   on    COTTON.  6 

day  in  summer  weather.    During  the  warmer  months  the  eggs  hatch 
in  about  four  days  after  being  laid. 
The  newly  hatched  red  spider,  called  the  Larva,  is  almost  round, 

has  si\  Legs,  and   is  nearly  colorless.      It   begins   feeding  at    once,  and 

(in  summer  time)  after  two  day-'  activity  it  becomes  quiet,  darkens 
in  color,  casts  it-  skin  for  the  first  time,  and  emerges  as  the  primary 
nymph  with  an  added  pair  of  Legs    making  eight. 

The  primary  nymph  becomes  Larger  in  size  and  darker  in  color, 
hut  gives  no  indication  of  sex.  Feeding  continues  ad  ively  and  at  the 
termination  of  another  two-day  period  (in  summer  months)  a  second 
molting  occurs  which  gives  rise  to  the  third  stage  -the  secondary 
nymph. 

With  this  last  nyinpnal  stage  the  first  indication  of  sex  appears. 
As  with  the  preceding  stage.-,  two  day--  usually  suffice  in  summer 
for  the  completion  of  this  period,  at  the  end  of  which  time  the 
skin  in  shed  for  the  third  time  and  at  last  the  perfectly  developed 
adult  mites  appeal-.  At  the  occurrence  of  each  molt  the  skin  splits  in 
two,  crosswise,  and  the  creature  crawls  out  of  the  two  halves.  The 
old  cast  skin-  are  usually  to  be  -ecu  in  abundance  among  the  fibrils 
of  the  web. 

THE    ADULT    MALES    AND    FEMALES   COMPARED. 

Concerning  the  relative  abundance  of  female-  and  males  it  may  be 
said  that  there  sixmus  to  be  a  predominance  of  females  throughout 
the  stimmer.  but  toward  the  approach  of  cold  weather  the  occurrence 
of  the  sexes  becomes  more  nearly  equal.  The  period  of  life  of  the 
adult  female  varies  from  17  days  in  midsummer  to  several  months 
in  winter.  The  male  i-  shorter  lived.  A-  before  stated,  the  female 
is  decidedly  larger  than  the  male,  more  rounded  behind,  and  of  a 
much  deeper  Color.  She  doe.-,  not  move  aboul  much,  and  when  she 
does  her  motion  is  rather  slow.  On  the  other  hand,  when  not  mating, 
the  male  i-  frequently  seen  moving  rapidly  about.  The  body  and 
are  well  besel  with  bristles,  which  arc  somewhat  more  con 
spicuous  in  tl'.e  mall-,  than  in  the  females.  The  eye-,  consisting  each 
of  two  Mil,-,  one  close  behind  the  other,  are  situated  near  the  front 
edge  of  the  body  directly  over  the  second  pair  of  legs. 

M  VTING. 

Almost  immediately  upon  becoming  adult,  the  red  spiders  mate 
aiul  begin  egg  laying.  The  males  seem  to  recognize  unfertilized 
female-  with  ease.  The  tir-i  eggs  are  frequently  deposited  on  the 
same  day  upon  which  the  transformation  occurs  from  the  last 
liymphal  to  the  adult   stage. 


THE   RED    SPIDER    ON    COTTON. 


PARTHENOGENESIS. 

Experiments  conducted  with  unmated  female  red  spiders  clearly 
proved  that  they  are  normally  capable  of  laying  eggs,  which  in  turn 
hatch  and  develop  into  mature  individuals.  No  tests,  however,  have 
been  successfully  conducted  to  determine  the  sexual  fertility  of  the 
latter. 

GENERATIONS. 

The  season  of  1911  at  Batesburg,  S.  C,  was  one  of  unusual  drought 
and  heat  and  there  were  about  17  generations  between  March  11  and 
November  5.  The  time  required  for  a  single  generation  varied  from 
35  days  in  March  and  early  April  to  10  days  throughout  most  of 
June,  July,  and  August,  and  to  25  days  in  the  greater  portion  of 
October  and  early  November.  The  following  table  presents  the 
duration  of  each  stage  of  each  of  the  17  generations: 

Table  I. — Development  of  generation*  of  the  cotton  red  spider. 


Gener- 
ation. 


1 

2. 
3 
4 
5 
ti 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 


l'eriod  covered  by  gerneration. 


Incuba- 
tion 
period. 


Mar.  11  to  Apr.  14. 
Apr.  15  to  Apr.  29. 
Apr.  30  to  May  13. 
May  14  to  May  25. . 
May  20  to  June  6.. 
June  7  to  June  17. 
June  IS  to  June  27. 
June  28  to  July  7.. 
JulvSto  July  18... 
July  19  to  July  28. . 
July  29  to  Aug.  7. . 
Aug.  8  to  Aug.  17.. 
Aug.  IS  to  Aug.  29. 
Aug.  30  to  Sept.  9. 
Sept.  10  to  Sept.  24 
Sept.  25  to  Oct.  10. 
Oct.  11  to  Nov.  4.. 

Average 


Days. 
13 
6 
6 
5 
5 

4.5 
4 
4 
4 
4 
4 
4 
5 
5 
5 
0 


5.5 


Larval 
period. 


Days. 
9 
3 
3 
3 
3 

2.5 
2 
2 

2.5 
2 
2 
2 

2.5 
2 

3.5 
3 
0 


3.1 


Nymph 

(1) 
period. 


Days. 
0 
3 
3 
2 
2 
2 
2 
2 

2.5 
2 
2 
2 
2 
2 
3 
3 
5 


Nymph 

(2) 
period. 


Days. 
7 
3 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 

2.5 
2 

3.5 
4 
5 


2.8 


Ovipo- 

sition  to 

adult. 


Days. 


35 
15 
11 
l-> 
12 
11 
10 
10 
11 
10 
10 
10 
12 
11 
15 
\i< 
25 


11 


RELATION    OF   WEATHER    TO   BREEDING    ACTIVITIES. 

The  influence  of  the  weather  on  breeding  activity  is  very  notice- 
able. Hot,  dry  conditions  greatly  favor  and  hasten  development. 
while  cool,  wet  weather  correspondingly  retards  it.  A  female  laying 
normally  about  6  or  7  eggs  per  day  will  often  upon  the  occurrence 
of  a  very  hot  day,  suddenly  increase  the  number  to  15  or  even  more 
eggs  per  day,  or  upon  a  chilly  day  may  drop  as  suddenly  to  1  or  2 
eggs.  It  is  easy  then  to  understand  the  remarkable  rate  at  which 
this  pest  increases  during  times  of  unusual  drought. 

OBSERVATIONS  ON    HABITS. 

In  establishing  herself  upon  cotton  the  female  selects  a  concave 
area  between  the  uinlcr  v"eins  of  the  leaf  and  begins  at  once  to  deposit 
e<s<^.  These  may  be  attached  to  the  fibrils  of  the  web  slightly  above 
the  surface,  or,  as  seems  most  often  the  case,  they  are  placed  directly 


THE    RED    SIMM  i;    <>N    rorinN. 


upon  the  Leaf.  The  eggs  are  usually  clustered  rather  closely  and 
rarely  occupy  an  area  greater  in  size  than  that  of  a  dime.  Feeding 
continues  interruptedly  throughout  the  period  of  egg  Laying  and  the 
affected  area  of  the  leaf  becomes  thickly  dotted  with  the  blackish- 
green  puncture  marks.  Meanwhile  a  wine-red  spot  has  appeared  on 
the  upper  surface  of  the  Leaf  directly  over  the  young  colony,  which 
spreads  as  the  colony  increases  and  may  finally  color  the  entire  Leaf. 
As  the  eggs  hatch  the  larva'  remain  close  to  the  place  of  their  birth. 
The  mite-  seem  of  a  decidedly  social  disposition.  In  a  young  colony 
there  is  usually  little  web  formed,  but  where  the  spiders  are  very 
abundant  the  web  may  become  quite  conspicuous.  It  doubtless 
afford-  some  protection  from  adverse  weather  conditions,  and  upon 
several  occasion-  hostile  insects  have  been  observed  ensnared  and  dead 
among  the  fibers.  New  females,  after  mating,  either  select  an  attrac- 
tive spot  on  the  leaf,  or  migrate  upward 
to  a  more  tempting  leaf,  or  in  some 
cases  may  even  travel  to  another  plant. 

THE  VIOLET  AS   HOST. 

When  cotton  dies  or  becomes  untempt- 
ing  in  the  late  fall  an  exodus  of  red 
spiders  from  the  cotton  fields  occurs  in 
the  effort  to  find  more  suitable  food 
plants.  At  this  time  cotton  mites  may 
be  easily  found  on  a  number  of  native 
and  cultivated  plants,  prominent  among 
which  are  cowpeas.  tomato.  Jamestown 
weed,  ironweed,  and  cultivated  violets. 
Most  of  these  plant-  die  after  the  frosts, 
but  the  violet  remains  somewdiat  green 
throughout  the  winter,  and  it  i-'  upon 
dii-  plant,  probably,  that  the  vast  majority  of  mites  overwinter.  Out 
of  many  cases  of  cotton  infestation  investigated  the  vast,  majority 
have  indicated  most  clearly  that  the  original  source  of  the  pest  was 
doubtless  this  innocent  pet  of  the  housewife,  the  English  violet. 
(See  fig.  •_'.) 

otiiki;    in '-is. 

In  all.  the  red  spider  ha-  been  found  in  1911  upon  over  50  species 
of  plants,  including  weed-,  ornamental  plants,  and  garden  and  field 
crop-.  Upon  most  of  these  the  pesl  was  only  occasionally  seen,  but 
it  wa-  found  commonly  throughout  the  active  season  upon  the  I'd 
lowing  plant-:  Beans,  oowpeas,  dahlia,  ironweed.  Jerusalem-oak 
Weil.  Jamestown  weed,  okra,  tomato,  wild  blackberry,  and  wild 
geranium. 


;•:;.'.  '•/•:•:•// ..;': 

o  O   O  0   o 

0  o 
o 

°-C3 

Pig,  -. — Diagram  showing  how  vio- 
lets growing  in  dooryard  give 
rise  to  rod  Bpider  infestation  in 
adjoining  field.  The  infestation 
is  most  severe  near  the  yard. 
This  diagram  is  typical  of  many 
cases  found  during  1911.  (Orig 
Inal.  i 


b  THE   RED    SPIDER    ON    COTTON. 

HIBERNATION    VERSUS    WINTERING. 

Some  observers  have  thought  that  the  red  spider  commonly  hiber- 
nates in  trash  or  in  the  soil  in  cotton  fields,  but  the  past  season's 
investigations  have  produced  absolutely  no  evidence  to  support  this 
idea.  During  the  early  spring,  before  the  active  season  for  the  red 
spider  commenced,  trash  was  several  times  taken  from  fields  in  which 
the  infestation  had  previously  been  severe  and  examined  with  great 
care.  A  few  minute  dormant  acarids  and  other  forms  were  thus 
obtained,  but  no  reel  spiders  could  be  found  in  such  material.  Simi- 
larly, during  December,  1911,  ample  quantities  of  trash,  etc.,  from 
recently  infested  fields  were  carefully  examined,  but  always  without 
finding  any  trace  of  the  red  spider.  That  this  pest  remains  more  or 
less  active  throughout  the  winter  there  can  be  no  doubt.  Mr.  G.  A. 
Runner  found  active  adults  at  Batesburg,  S.  C,  on  December  21, 
1909.  Mr.  H.  F.  Wilson  observed  red  spiders  feeding  in  early  Feb- 
ruary at  the  same  locality.  The  writer  found  all  stages  on  violets  on 
March  11,  and  adults  as  late  as  December  19,  on  the  same  host  at 
Batesburg.  The  finding  of  the  active  red  spiders  during  the  coldest 
weather  is  certainly  an  additional  indication  that  hibernation  doe? 
not  take  place  in  South  Carolina. 

DISPERSION. 

How  do  red  spiders  become  established  upon  cotton?  They  have 
no  wings  and  their  legs  are  very  minute.  Close  observations  reveal 
that  on  the  ground  they  normally  travel  at  the  rate  of  1  inch  per 
15  seconds,  which,  if  maintained,  would  total  480  feet  in  24  hours. 
Red  spiders  are  doubtless  occasionally  transferred  by  dogs,  chickens, 
other  domestic  animals,  insects,  and  birds.  Strong  winds  ma}'  serve 
occasionally  to  transfer  them  from  plant  to  plant.  It  is  the  writer's 
firm  belief,  however,  that  the  chief  means  of  dispersion  is  the  red 
spider's  own  efforts.  When  once  established  in  a  field  they  may  be 
further  distributed  by  farm  hands  and  by  stock  while  cultivation  is 
being  carried  on.  They  also  spread  from  plant  to  plant  along  the 
interlacing  branches,  but  traps  specially  prepared  with  "  tangle-foot  " 
and  placed  in  the  field  have  proven  that  individuals  commonly  crawl 
from  plant  to  plant  by  way  of  the  stalk  and  the  ground. 

Since  the  red  spider  apparently  uses  no  instinct  or  intelligence  in 
finding  cotton  plants,  it  follows  that  the  pest  must  hit  upon  the  cotton 
stalks  entirely  by  chance.  The  result  of  this  haphazard  manner  of 
migration  must  necessarily  result  often  in  the  penetration  of  the 
spiders  far  into  the  center  of  fields,  thus  giving  rise  to  the  mistaken 
impression  that  they  had  hibernated  at  these  points. 

Furthermore,  as  the  likelihood  of  the  discovery  of  cotton  by  the 
spider  is  doubtless  in  proportion  to  the  thickness  of  the  '"stand,"  it 


THE    RED   SPIDER    ON   COTTON.  / 

should  follow  that  the  thick  broadcasting  of  a  narrow  border  strip 
along  tlif  edge  of  a  field  adjoining  a  source  of  infestation  would  serve 
as  a  trap  crop  to  intercept  the  majority  of  migrating  spiders.  This 
strip  should  be  plowed  in  as  soon  as  there  seems  to  be  danger  of  a 
general  movement  to  the  main  held.  (For  a  practical  te.st  of  this 
idea,  see  under  Prevention,  p.  10.) 

NATI    BE     OF     I)  \M.UiK. 

Cotton  seedlings  2  inches  bigh  were  found  infested  on  .May   1.  but 
not  until  dune  1  did  the  work  of  the  pest  become  noticeable.      The 


I  — a,  Cross  '  normal  cotton  leaf;  h.  cross  section  of  cotton  leaf  Injured  by 

the    red    spider.     The    puncture    Is    near    lower    right-hand    corner.      Highly    magnified, 
oal.  i 

presence  of  the  pest  on  cotton  is  first  revealed  by  the  appearance  on 
the  upper  surface  pi  the  leaf  of  a  blood-red  spot.  A.s  leaves  become 
badly  infested  they  redden  over -the  entire  surface,  become  distorted, 
and  drop.  The  lower  leaves  are  first  attacked,  but  infestation  spreads 
upward  until  often  only  the  bare  stalk  and  one  or  two  terminal 
leave-  remain.  Such  plants  almost  invariably  die.  The  injury  to 
the  leaf  and  the  discoloration  which  follow-  the  feeding  of  the  mites 
are  easily  understood  by  referring  to  figure  '■'>.  which  represents  (a) 
the  appearance  of  healthy  cotton  leaf-tissues  and  (&)  the  condition 
of  the  tissue  after  feeding  In  the  pest.  A-  previously  intimated,  the 
worsl  spots  of  infestation  are  usually  to  be  found  in  close  proximity 


8  THE   BED    SPIDER    ON    COTTON. 

to  yards  with  borders  of  violets.  Large  fields  are  probably  never 
completely  damaged,  but  small  fields  frequently  become  wholly 
affected.  The  crop  of  one  5-acre  field  near  Leesville,  S.  C,  was 
probably  reduced  at  least  50  per  cent  by  this  pest.  Local  spots  with 
from  25  to  100  per  cent  damage  are  frequently  to  be  seen. 

NATURAL   CONTROLLING   AGENCIES. 

Red  spider  occurrence  was  most  severe  throughout  July  and  was 
still  at  its  height  on  August  1.  Within  three  weeks  of  the  latter 
date,  however,  the  pest  had  become  so  greatly  diminished  that  it  was 
hardly  noticeable  and  was  doing  practically  no  damage.  This 
phenomenon  indeed  happened  suddenly,  and  the  agencies  which 
worked  to  produce  it  are  unquestionably  of  great  economic  value. 
The  toughening  of  the  leaves  at  that  time  may  have  caused  many 
mites  to  desert  cotton  for  other  plants,  but  another  factor  of  much 
more  importance  was  the  appearance  in  abundance  of  several  species 
of  insect  enemies. 

CLIMATIC    INFLUENCES. 

As  before  mentioned,  climatic  conditions  exert  a  marked  influence 
upon  the  welfare  of  the  pest.  During  times  of  little  rainfall  and 
high  temperature  reproduction  goes  on  by  leaps  and  bounds;  on 
the  other  hand,  long,  heavy  rains  work  havoc  to  the  red  spider 
population.  In  spite  of  the  fact  that  the  red  spiders  inhabit  the 
underside  of  the  leaves,  many  are  washed  off  by  rains  and  many  more 
are  destroyed  by  the  upward  bombardment  of  sand  particles,  which 
may  always  be  seen  coating  the  lower  leaves  after  storms.  From 
observations  made  both  early  in  the  season  and  at  the  beginning  of 
winter  it  is  doubtless  true  that  the  young  stages  are  killed  by  freez- 
ing weather.  This  naturally  prevents  any  considerable  winter  in- 
crease, and  in  addition  many  adults  probably  perish. 

INSECT    ENEMIES. 

Hot  weather,  although  favoring  red-spider  development,  also  en- 
courages the  increase  of  insect  enemies,  of  which  several  have  been 
observed.  Were  it  not  for  these  inconspicuous  friends  of  the  farmer 
the  depredation  to  his  crops  by  the  red  spider  would  unquestionably 
be  far  more  severe.  The  following  are  a  few  of  the  more  important 
beneficial  species  observed  this  season  at  Batesburg,  S.  C. 

Triphleps  insidivsus  Say  (fig.  1),  a  small  anthrocorid  bug,  was 
seen  from  the  beginning  of  August,  and  both  in  the  nymphal  and 
aduli  stages  was  probably  the  most  effective  enemy  of  the  spider. 
Coming  upon  a  red  spider  like  a  flash,  the  adult  thrusts  its  sharp 
proboscis  through  the  pest's  back  and  proceeds  quietly  to  siphon  out 


Till-    i:ii'   S1UD1  R   ON    COTTON. 


Fig.  4. — Triphlepa  Insidiosus,  sxu  important  enemy  of  tbe 
red  spider.     Much  enlarged.     (Original.) 


tin-   body   contents.     The   first    victim   observed    was  "drained'1   in 

about  five  minutes,  but  each  succeeding  meal  was  of  shorter  dun 

as  the  appetite  became 

satisfied.      The   actions 

dt'  the  nymph    (fig.  5) 

arc  similar,  but  the  in- 
dividuals observed  were 

seen    only    to    destroy 

eggs  of  the  spider.     In 

this  operation   the  pro- 
boscis was  not    inserted 

far  into  the  ovum,  and 

two  minutes  sufficed  for 

draining  an  egg. 

A    species    of    Chry- 

sopa  or  lace-winged  fly 

was     seen     abundantly 

throughout  most  of  the 

summer,    the    larva    of 

which  is  doubtless  very  active  in  reducing  the  pest. 
Two  species  of  thrips,  Eutkrips  ftcscus  Hind-  and  E.  occidentals 

Pergande,  have  been  determined  this  season  from  cotton.     They  are 

commonly  found  throughout, 
the  season  about  red  spider 
colonies,  and  may  be  very  in- 
strumental in  spider  destruc- 
tion. Srolothrips  sexmacidata 
Pergande  has  been  recorded  as 

• 

an  enemy  of  the  red  spider  by 
Pergande  and  by  Dully. 

Lady-beetle  larvae  and  adults 
of  several  species  were  com- 
monly seen  on  infested  Leaves. 
These  were  usually  either 
I  .,, ,  irn  lla  9-notata  I  Ib-i.  or 
Hippodamia  convt  rg>  ns  Guer., 
Init      a      small     black     species, 

§  i/ni nil*)  st,  thorus  i 
1  ..'!•..  n  as  occasionally  observed. 
The  larger  beetles  were  prob- 
ably more  intent  upon  cotton  aphides,  but  the  last-mentioned  sp< 
although  late  in  appearing  and  not  very  numerous,  seems  to  be  more 
restricted  to  the  cotton  mite  than  arc  other  spe 


/    \p)  I ■  :.  ■    ina  d •  ■    Nymph, 

Greatly  enlarged.     (Original.) 


10  THE    RED    SPIDER    ON    COTTON, 


REMEDIAL   MEASURES. 


PREVENTION. 


Control  on  violets. — First  among  preventive  measures  against  the 
red  spider  is  that  of  its  control  on  violets.  In  most  cases,  as  before 
stated,  infested  cotton  fields  upon  examination  are  found  to  have 
near  them  infested  violet  borders.  In  early  June  of  the  past  season, 
in  one  particular  instance,  violets  adjoining  fields  of  past  severe 
annual  infestation  were  thoroughly  sprayed.  It  is  of  great  interest 
to  record  that  subsequent  infestation  in  these  fields  was  practically 
negligible.  These  and  similar  observations  certainly  emphasize  the 
important  part  that  the  violet  plays  in  the  seasonal  history  of  the  red 
spider. 

( '/( an  culture. — Borders  of  weeds  and  underbrush  about  fields 
should  be  burned  or  grubbed  out.  Margining  a  field  close  to  a  spot 
which  was  heavily  infested  the  previous  season  there  was  found  to 
occur  a  thick  border  of  wild  geranium,  dock,  and  other  weeds  which 
at  that  time  contained  many  red  spiders.  These  weeds  were  de- 
stroyed by  burning  over  them  a  heavy  application  of  straw.  No 
spiders  appeared  in  the  adjoining  cotton  throughout  the  season. 

Broadcasted  cotton. — An  opportunity  was  accidentally  provided  of 
testing  the  value  of  thickly  broadcasting  cotton  at  the  boundary  of 
a  field  as  a  trap  crop  for  red  spiders.  This  cotton,  intended  as  a 
cover  crop,  intervened  between  the  cotton  field  proper  and  a  large, 
heavily  infested  border  of  violets — a  former  abundant  source  of 
migration.  The  broadcasted  cotton  became  infested  and  was  later 
plowed  in.  The  adjoining  field  remained  free  from  mites.  The  suc- 
cess of  this  experiment  would  strongly  indicate  that  the  cotton  trap 
crop  is  one  of  the  most  practical  cultural  expedients  to  be  used  in 
controlling  this  pest. 

Spacing. — Experiments  at  Batesburg,  S.  C.  have  shown  that  the 
reel  spider  commonly  travels  between  plants  upon  the  ground.  This 
shows  the  futility  of  spacing  as  a  remedial  measure. 

Time  of  planting. — The  advantages  of  early  or  of  late  planting 
are  not  sufficiently  clear  to  justify  serious  consideration.  It  would 
seem  reasonable,  however,  to  suppose  that  early  planting  would  en- 
able the  plants  to  attain  greater  size  and  vigor  by  the  time  of  the 
appearance  of  the  spiders  and  that  this  would  perhaps  assist  the 
plants  in  withstanding  the  weakening  effects  of  the  pest. 

Rotation. — In  an  effort  to  test  the  rotational  value  of  other  crops, 
cow-peas,  corn,  beets,  and  peanuts  were  planted  in  or  near  infested 
areas.  In  addition,  grains,  beans,  peas,  onions,  tomatoes,  squash, 
watermelon,  okra,  turnip,  lettuce,  and  other  vegetables  in  infested 
locations  have  been  observed  frequently.  Excepting  the  grains  and 
peanuts,  the  red  spider  has  been  seen  commonly  upon  all  of  these. 


THE    BED   BPIDEB   ON    COG  CON.  11 

On  the  other  hand,  should  an  immune  crop  be  found  and  employed, 
it  is  extremely  probable  that  the  pes!  would  reinvade  the  fields  upon 
the  return  to  <-<>tton  culture  with  as  irivat  ease  ami  quickness  as  it 
has  done  during  any  previous  season,  providing  the  sources  of  infesta- 
tion were  yel  at  hand.  Rotation,  then,  does  not  promise  to  contribute 
toward  the  solution  of  the  problem. 

Effects  of  fertilizers.  A  rather  elaborate  series  of  tests  with  fer- 
tilizers was  instituted  in  an  attempt  to  determine  whether  the  various 
applications  assisted  cotton  to  withstand  the  injurious  effects  of 
infestation.  Since  almost  no  infestation  appeared  in  these  test  plats 
it  was  impossible  to  deduce  positive  conclusions,  l!  was  very  notice- 
able, however,  that  plant-  receiving  heavy  applications  withstood  the 
very  severe  droughl  conditions  which  prevailed  in  South  Carolina  in 
11)11  conspicuously  better  than  did  plant-  which  were  not  so  treated. 
It  seems  reasonable  to  suppose,  therefore,  that  plant-  which,  have 
U'en  fortified  bj  a  libera]  quantity  ol'  fertilizer  will  be  assisted,  upon 
occurrence  of  severe  infestation,  in  resisting  it-  effects. 

l;l  PRESSION. 

We  have  just  discussed  cultural  measures  which  may  help  to  pre- 
vent infestation.  We  will  now  consider  what  may  he  done  to  combat 
the  pest  when  it  has  already  gained  entrance  to  a  field. 

Pulling  infested  plants. — The  experiment  was  made  in  one  Held  of 
pulling  up  and  destroying  the  first  few  plant-  which  -bowed  infesta 
tion.  In  thi>  particular  case  the  operation  was  repeated  three  times. 
Care  was  taken  to  find  every  plant  showing  the  characteristic  red 
spots,  and  these  were  carried  from  the  field  and  burned.  The  result 
was  most  satisfactory,  and  the  pest  was  completely  eradicated. 

[f  infestation  has  spread  until  a  considerable  patch  has  become 
involved  it  might  be  advisable,  in  the  case  of  a  large  Held,  to  plow 
up  the  a  fleet  ed  portion  in  order  to  save  the  balance  of  the  field.  Such 
a  drastic  measure,  however,  should  only  be  resorted  to  in  extreme 
cases,  and  the  planter  concerned  must  he  the  judge  of  its  desirability. 

Insecticides.—  In  all.  l'<'>  spray  combinations  were  thoroughly  tested 
under  conditions  entirely  natural.  The  field  used  for  this  purpose 
was  ahoitt  1  acre  in  extent,  and  infestation  had  become  both  verj  gen- 
eral and  very  severe.  A  strip  through  the  middle  of  the  field,  crossing 
each  sprayed  plat,  was  left  unsprayed  to  serve  a-  a  cheek.  Since  no 
substance  was  discovered  which  could  safely  he  used  i"  destroy  all 
eggs  in  one  application,  it  was  found  necessary  to  spray  twice  with 
an  interval  of  -ix  or  -even  days,  so  a-  to  destroy  the  hatching  larvae. 
The  killing  ability  of  all  these  sprays  was  computed,  and  the  per- 
centages range  from  100  to  0.  Each  of  the  following  six  combina- 
tions (see  Table  II)  wa-  found  to  be  very  satisfactory.  These  are 
presented  to  indicate  the  manner  of  preparation,  together  with  the 


12 


THE   RED    SPIDER   ON    COTTON. 


cost  of  100  gallons  of  each.  If  one  of  these  were  to  be  used  in 
preference  to  all  others  it  should  undoubtedly  be  potassium  sulphid. 
This  insecticide  commends  itself  from  every  standpoint — cheapness, 
simplicity  of  preparation,  continued  readiness  for  use,  ability  to  kill 
quickly,  and  safety  of  foliage.  Altogether  it  seems  to  be  an  ideal 
red-spider  spray.  It  was  found  that  100  gallons,  when  applied  as  a 
misty  spray,  about  sufficed  to  treat  an  acre  of  average-sized  cotton. 

Table  II. — Some  satisfactory  sprays  for  the  red  spider. 


Spray 
No. 


I 
II 

III 
IV 

V 

VI 


Formula  and  items. 


Potassium  sulphid,  3  pounds,  at  25  cents 

Water,  100  gallons. 

Flowers  of  sulphur,  15  pounds,  at  4  cents]  | $0. f>0 

Fresh  lime,  20  pounds,  at  4  cents /boiled< 80 

Water,  100  gallons )  (  

Miscible  oil,  5  gallons,  at  $1 

Water  to  make  100  gallons  (1  to  20). 

Potassium  permanganate,  16|  pounds,  at  50  cents 

Water  to  make  100  gallons  (2  per  cent  solution). 

Miscible  oil,  2\  gallons,  at  $1 $2. 50 

Black-leaf  tobacco  extract,  40%,  £  gallon,  at  $1.25  per  pound 2. 00 


Flowers  of  sulphur,  28  pounds,  at  4  cents $1. 12 

Soft  soap,  14  ounces,  at  40  cents  per  pound 35 

Water  to  make  100  gallons.  


Total 
cost. 


$0.75 

1.40 
5.00 

8.25 
4.50 


Per  cent 
killed. 


100 
100 

100 


99 


SI   .M.MARY. 

The  female  red  spider,  appearing  to  the  naked  eye  like  a  dot  of 
reddish  ink  from  the  point  of  a  fine  pen,  lays  about  50  or  60  round, 
colorless  eggs,  which  hatch  in  summertime  in  about  four  days. 

The  colorless,  newborn  spider  has  six  legs,  feeds  at  once,  and  molts 
in  two  days  to  the  primary  nymph. 

This  first  nymphal  stage  (and  all  later  stages)  possesses  eight 
legs,  and  has  become  larger  in  size  and  darker  in  color.  In  two  more 
days  (in  summer)  it,  in  turn,  molts  to  the  secondary  nymph. 

The  second  nymphal  stage  lasts  two  days,  at  the  end  of  which 
time,  after  molting,  the  fully  formed  adult  emerges.  Mating  occurs 
at  once  and  egg  laying  commences  immediately  afterwards. 

Thus,  one  generation  requires  in  summer  weather  in  South  Caro- 
lina about  10  or  11  days.  There  are  probably  about  15  generations 
in  an  average  year  in  that  locality. 

The  red-spider  colonies  live  on  the  underside  of  the  cotton  leaves, 
and  their  constant  feeding  causes  blood-red  spots  to  appear  on  the 
tops  of  the  leaves.  The  effect  upon  the  cotton  plant  is  that  the 
leaves  drop,  one  by  one,  until  usually  the  plant  dies. 

The  pest  increases  and  spreads  most  rapidly  in  hot,  dry  weather 
until  (toward  the  end  of  July)  several  acres  of  a  field  may  become 
badly  damaged. 


THE    RED   SPIDEB    OK    COI  CON.  l;i 

Several  insects  have  been  discovered  which  destroy  many  mites, 
and  are  thus  of  great  benefil  to  the  planter. 

At  the  end  of  the  cotton-growing  season  most  of  tin-  red  spiders 
migrate  afoot  in  search  of  greener  plants,  the  majority  of  those 
which  survive  settling  ultimately  upon  the  cultivated  violet. 

RECOMMENDAl  [ONS. 

(1)  Clean  culture. — Burn  or  grub  out  all  weeds  and  underbrush 
about  cotton  Gelds  and  practice  fall  plowing  so  far  as  possible. 

[..')  Control  on  violets.  -Spray  or  destroy  suspected  riolet  plants 
in  order  to  remove  the  sources  of  red  spider  infestation. 

(3)  Broadcasted  trap  borders. — Thickly  so'w  cotton  along  mar- 
gins of  fields  at  point-  where  infestation  has  appeared  on  former 
occasions,  ami  plow  these  in  about  June  1.  so  a-  to  intercept  and 
destroy  the  invading  mites. 

I/)  Pulling  "first  infested  stalks. — Maintain  a  careful  watch  of 
fields  so  that  the  first  attacked  plants  may  l>e  detected,  removed,  and 
burned,  thus  preventing  further  spread. 

(5)  Spraying. — Apply  one  of  the  insecticide--  recommended  above 
to  the  infested  portion  of  a  field  before  occurrence  becomes  too  gen- 
eral to  prohibit  its  use.  Two  application-  should  be  made;  the  first 
to  destroy  the  living  mites,  and  the  second,  a  week  later,  to  kill  the 
recently  hatched  individual--  which  were  eggs  at  the  time  of  the  first 
spraying. 

finally,  the  opinion  will  be  ventured  that  the  red  spider  is  not  a 
difficult  pesi  to  combat.  Unlike  many  other  pests,  it  has  no  wings 
and  spread-  mainly  by  means  of  it-  tiny  legs.  Migration  does  not 
extend  far  from  its  winter  quarters.  This  make-  every  man*-  prob- 
lem virtually  his  own.  In  other  words,  if  hi-  infestation  ha-  always 
come  from  a  certain  spot  upon  his  premises,  proper  attention  to  this 
spot  will  yield  him  results  in  spite  of  the  negligence  of  his  neighbors. 

Approved  : 
James  Wilson, 

>.  ( /,  tary  ,>i  .  [grit  ultu 

Washington,  D.  ('..  February  I',.  1012. 


UNIVERSITY  OF  FLORIDA 


II    II 


3  1262  09216  5967 


